Improvement in processes for obtaining chromates



UNITED STATES PATENT QFFIGE.

JAMES C. BOOTH, OF PHILADELPHIA, PETSNSYLVANIA.

IMPROVEMENT IN PROCESSES FOR OBTAINING CHROMATES.

Specification forming part of Letters Patent No. 9,853, dated July 19, 1653.

To all whom it mag concern:

Be it known that I, JAMES (J. BOOTH, of the city and county of Philadelphia, and State of Pennsylvania, have invented a new and Improved Mode of lvlannfacturiug Uhromate and Bichromate of Potash from Ghromic Iron or Chrome Ore; and I do hereby declare that the following is a full and exact description.

Chrome ore is composed chiefly of oxide of chrome and oxide of iron.

The ordinary mode of obtaining chromate and bichromate of potash from chrome ore is by the repeated heating of the chrome ore together with carbonate of potash. Sometimes saltpeter is added; but the operation is sometimes effected without saltpeter. The chemical reaction which takes place during this operation is well known. The oxide of chrome contained in the chrome ore is oxidized and converted into chromic acid, and this chromic acid combines with the potash in the carbonate of potash, forming chromate of potash, while carbonic acid is liberated. The oxide of iron and the chrom ate of potash are then separated by lixiviation. This process of making chromate of potash requires that the ore should be thus heated several timesin succession with fresh portions of carbonate of potash,

for a portion only of the oxide of chrome is oxidized and separated from the ore at a single heating.

The nature of my invention consists in reducing the oxide of iron in chrome ore, either wholly or in part, by means of carbon in any of its several forms, or by means of any of its compounds which are or may be employed as fuel-sueh as carbonic acid, carbureted hydrogen-as the first stage of the manufacture; and, secondly, in removing the iron so reduced by means of sulphuric acid. The remainder of the process of manufacture is similar to that which was described above as now musenamely, to heat the residue obtained by my improved process in contact with carbonate of potash, and either with or without saltpeter.

To enable others skilled in the art to use my improvement, I will describe more minutely the mode of applying my improvement which Ihave found to answer best, without intending to limit myself to the peculiar proportions of acid specified, or form or proportions of carbon.

1 take the ore known as chromic iron or chrome ore and grind it to a powder by the usual mechanical means. I mix the powdered ore with about one-fit'th'of its weight of powdered charcoal. This mixture is placed upon the hearth of a reverberatory furnace constructed as the reverberatory furnaces for reheating or puddling iron are ordinarily constructed-that is, so that the heat or flame may be as free as practicable from free oxygen or atmospheric air. By this operation the greater part or all of the oxide of iron in the chrome ore is reduced to the metallic state. When one charge of the mixture is reduced, as above described, it is raked out and a second charge of the mixture introduced into the heated furnace, reduced, and replaced by 'a third, and so on. Each charge, when raked out of the furnace, is thrown into dilute sulphuric acid contained in vats, whereby the iron is dissolved, formmg a solution of protosulphate of iron or copperas. This solution, still containing free acid, is drawn off and run upon a fresh charge of reduced ore, in order more fully to saturate the free acid, after which itis again drawn off and evaporated to crystallization, so as to produce copperas in a state adapted to commerce. The residue in the vats is well washed with water and dried. It is then mixed with carbonate of potash, or with carbonate of potash and saltpeter, and heated in the same manner that the chrome ore itself is in the first instance heated in the process usually employed, and described above.

The following are the advantages of my improved process: By the usual mode of manufacturing chromate and bichromate ot' potash only a portion of the oxide of chromcisoxidized and chromate of potash formed by a single heating, and thus repeated heating with fresh portions of potash is required. These repeated heatings with potash involve a considerable loss of potash by volatilization. By the'employment of my process the first heating with carbonate of potash converts all, or nearly all, the oxide of chrome into chromate of potash, andthusmuchofthislcssbyvolatilization ofthe potash is avoided. The production of copperas, incident to my process, assists in defrayin g the expense involved in my process. The quantity of oil of vitriol 1 employ is nearly equal in weight to about two thirds of the weight of the ore itself.

The process precisely as above described experiment has led me to believe to be the most cite or bituminous coal, or any other carbonaceous fuel or carbonaceous material may be used; and instead of afurnace gas-retorts may be used.

The solution obtained by washing" the residue of the ore after the sulphate of iron is produced may be again economically used for diluting the acid which is to be applied to'remove another portion of iron from asucceeding charge.

I do not desire to claim separately as my invention such portion of the process hereinbefore described as I have stated to be similar to that now in use for manufacturing ch romate and bichromate of potash; but

What I do desire to claim as my invention, and to secure by Letters Patent, is

1. The reduction of chrome ore by the earv Witnesses:

GEORGE HARDING, JNo. E. SHAW. 

